Electron localization regulated by confined Co₃O₄ enhances electrocatalytic nitrate reduction to ammonia

Nitrate pollution poses a severe threat to aquatic ecosystems and human health. Although electrocatalytic nitrate reduction to ammonia (NITRR) has emerged as a sustainable pathway, sluggish multielectron transfer is a key obstacle for efficient NITRR, limiting its practical application. In this paper, electron localization regulated by Co₃O₄ confined in carbon nanotubes (Co₃O₄-in-CNTs) promoted the adsorption and activation of key intermediates, significantly enhancing NITRR performance. Co₃O₄-in-CNTs exhibited remarkable ammonia selectivity (94.0 %) and Faradaic efficiency (95.0 %) in a neutral electrolyte, achieving a high NO₃^⁻-N removal rate of 97.8 % at -0.5 V (vs. RHE). Multiscale structural and electronic analyses reveal that the confined structure enhanced charge transfer between the *NO₃ and Co₃O₄, allowing for boosted NITRR kinetics. Theoretical calculations demonstrate that the high localized electron density around Co₃O₄-in-CNTs can facilitate orbital coupling of d-Co₃O₄ and *NO₃, reducing the barrier. This study recovers ammonia as high-purity NH₄Cl, providing both a promising strategy for designing highly active NITRR catalysts and a practical way for the efficient removal of nitrogen pollutants and the conversion to valuable ammonia products.